КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 1, с. 19-27
УДК 541.49
THREE NAPHTHOATE-BASED CADMIUM(II) COMPLEXES WITH DISCRETE BINUCLEAR, CYCLIC TETRANUCLEAR, AND POLYMERIC DOUBLE-CHAIN MOTIFS
© 2015 P. X. Dai1, E. C. Yang2, *, and X. J. Zhao2, *
1 College of Chemistry & Environmental Science, Shaanxi University of Technology, Hanzhong, Shaanxi, 723001 P.R. China 2 College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of Inorganic-Organic Hybrid Functional Material Chemistry, Ministry of Education, Tianjin Normal University, Tianjin, 300387P.R. China *E-mail: encui_yang@163.com Received May 29, 2014
Three new naphthoate-based cadmium(II) complexes, [Cd2(Phen)2(NA)4] (I), [Cd4(H2O)2(2,2'-Bipy)2(NA)8] (II), and [Cd3(4,4'-Bipy)2(NA)6]n (III) (NA- = 1-naphthoate, Phen = 1,10-phenanthroline, 2,2'-Bipy = = 2,2'-bipyridine, and 4,4'-Bipy = 4,4'-bipyridine), were hydrothermally synthesized by varying the N-hetero-cyclic coligands and characterized by X-ray single-crystal structure analysis (CIF files CCDC nos. 971968 (I), 971969 (II) and 971970 (III)). Structural analyses reveal that the former two samples are carboxylate aggregated oligomers with centrosymmetric binuclear and cyclic tetranuclear motifs. By contrast, complex III exhibits a polymeric one-dimensional double-chain with linear {Cd3(NA)6} subunits periodically extended by pairs of ditopic 4,4'-Bipy connectors. Obviously, the mixed ligands of the self-assemble system play different roles with the core-aggregation for carboxylate group and the extension/termination of the subunit for N-heterocyclic coligand. Furthermore, all the three entities with higher thermal stability display strong fluorescent emissions at room temperature resulting from the NA--based intraligand and/or ligand-to-metal charge transfer, suggesting their hopeful use as fluorescent materials.
DOI: 10.7868/S0132344X15010028
INTRODUCTION
Rational design and successful preparation of functional metal complexes have always attracted intense interest mainly due to their structural and topological diversities [1, 2] as well as their potential applications in gas sorption [3], catalysis [4], magnetism [5] and luminescence [6]. In this field, mixed-ligand systems bearing polycarboxylate and bipyridyl-like binding groups and diverse metal ions have always generated lots of intriguing high-dimensional metal complexes with polynuclear metal cluster, inter-/self-penetrating and/or high-connected motifs [7—10]. Crystallographically, binding mode, number, as well as the position of the deprotonated carboxylate and pyridyl moieties can significantly dominate the fundamentally structural motif and the connectivity of the targeted complex. In particular, the unexpectedly synergistic coordination coming from the polycarboxylate group to the metal ion is observed to play more important roles for the resulting structural diversity and complexity, which has becoming one of essential factors for the targeted complexes. Many complex systems also demonstrate that the introduction of N-donor ancillary ligands, such as 2,2'-bipyridine-like chelating ligands or 4,4'-bipyridine-like bridging linkers [7, 11, 12], into
metal-carboxyl coordination systems will affect the architectures of the final coordination compound. To further investigate the influence of auxiliary co-ligands on the structures and properties ofcarboxylate-based coordination complexes, herein, three typically N-heterocyclic co-ligands, 1,10-phenanthroline (Phen), 2,2'-bipyridine (2,2'-Bipy), and 4,4'-bipyridine (4,4'-Bipy), were chosen as fundamentally building blocks to self-assembly with 1-naphthoic acid (HNA) and inorganic cadmium(II) salt. The main purpose for choosing HNA as a core-ligand is that deprotonated 1-naphthoate (NA-) with a three-atom carboxylate attached on a bulky n-conjugate skeleton can act as a functional organic ligand to generate interesting metal complexes by carboxylate coordinating with metal ion and also by weak n-n stacking interactions [13-15]. As a result, three novel NA--based Cd(II)-complexes, [Cd2(Phen)2(NA)4] (I), [Cd4(H2O)2(2,2'-Bipy)2(NA)s] (II) and [Cd3(4,4'-Bipy)2(NA)6]„ (III), were hydrothermally obtained and structurally characterized. Structural analysis reveals that the former two complexes are discrete oligomers with carboxylate aggregated bi- and tetranuclear motifs. By contrast, complex III exhibit polymeric double-chain with linear {Cd3(NA)6} subunits infinitely extended by ditopic 4,4'-Bipy connectors. Obviously, the
carboxylate group in I—III is consistently responsible for the aggregation of the discrete metal ion and the N-heterocyclic coligand contributes to the extension and/or termination of the structural subunits. Additionally, the three solid samples with higher compositional stability up to 230°C display strong fluorescent emissions at room temperature, which is primarily resulted from the NA--based intraligand and ligand-to-metal charge transfer.
EXPERIMENTAL
Reagents and instruments. HNA was purchased from Acros and other analytical-grade starting materials were obtained commercially and used as received without further purification. Doubly deionized water was employed for the conventional synthesis. IR spectra were collected in a range of 4000—400 cm-1 region on a Nicolet IR-200 spectrometer with KBr pellets. Elemental analyses for C, H, and N were determined on a PerkinElmer 2400C elemental analyzer. TGA experiments were carried out on a Shimadzu simultaneous DTG-60A thermal analysis instrument with a heating rate of 8°C min-1 from room temperature to 800°C under a nitrogen atmosphere (flow rate 10 mL min-1). Fluorescence spectra of the polycrystalline powder samples ofI-III were performed on a Fluorolog-3 fluorescence spectrophotometer from Horiba Jobin Yvon at room temperature.
Synthesis of I. A mixture of HNA (68.9 mg, 0.4 mmol), Phen (39.6 mg, 0.2 mmol), Cd(NO3)2 ■ 4H2O (123.4 mg, 0.4 mmol), NaOH (24.0 mg, 0.6 mmol), and doubly deionized water (12.0 mL) were sealed in a 23.0 mL stainless steel vessel and heated at 160°C for 120 h under autogenous pressure. After the mixture was cooled to room temperature at the rate of 5°C h-1, colorless block-shaped crystals suitable for single-crystal X-ray diffraction analysis were isolated directly, washed with ethanol, and dried in air. The yield was 35% based on HNA ligand.
For C34H22N2O4Cd
anal. calcd., %: Found, %:
C, 64.32; C, 64.30;
H, 3.49; H, 3.45;
N, 4.41. N, 4.35.
IR (v, cm-1): 3062 v(C-H), 1553 vas(COO), 1512 vas(COO), 1427 vs(COO-), 1407 vs(COO-), 1372 vs(COO).
Synthesis of II. Colorless block-shaped crystals suitable for single-crystal X-ray diffraction analysis were obtained by adopting the similar procedures to those of I only with 2,2'-Bipy instead of Phen. The yield was 40% based on HNA ligand.
For C54H3SN2O9Cd2
anal. calcd., %: Found, %:
C, 59.85; C, 59.78;
H, 3.53; H, 3.60;
N, 2.58. N, 2.47.
IR (v, cm-1): 3257 vAr(O-H), 3049 v(C-H), 1598 vas(COO), 1554 vas(COO ), 1437 vs(COO), 1407 vs(COO), 1373 vs(COO).
Synthesis of III. Colorless block-shaped crystals suitable for single-crystal X-ray diffraction analysis were obtained by adopting the similar procedures to those of I only with 4,4'-Bipy instead of Phen. The yield was 30% based on HNA ligand.
For C86H58N4O12Cd3
anal. calcd., %: C, 61.61; H, 3.49; N, 3.34. Found, %: C, 61.50; H, 3.41; N, 3.27.
IR (v, cm-1): 3049 v(C-H), 1604 vas(COO), 1546 vas(COO), 1507 vas(COO), 1412 vs(COO), 1374 vs(COO).
X-ray diffraction analysis. Single-crystal X-ray diffraction data for I—III were collected on a computer-controlled Bruker APEX-II CCD diffractometer equipped with graphite-monochromated MoZ„ radiation with radiation wavelength 0.71073 Â by using
9 scan mode at room temperature. Semiempirical multiscan absorption corrections were applied using SADABS [16] and the program SAINT [17] was used for integration of the diffraction profiles. Both structures were solved by direct methods and refined with the full-matrix least-squares technique using the SHELXS-97 and SHELXL-97 programs [18]. Aniso-tropic thermal parameters were assigned to all non-hydrogen atoms. The organic hydrogen atoms were generated geometrically. Details for crystallographic data were listed in Table 1, and selected bond lengths and angles were given in Table 2. Hydrogen-bonding parameters for II and III were shown in Table 3. Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (nos. 971968 (I), 971969 (II) and 971970 (III); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
Phase-pure crystals of I—III were successfully prepared under similar hydrothermal conditions in basic medium. Obviously, the introduction of aqueous NaOH solution is to make HNA ligand deprotonation and facilitate its coordination with Cd2+ ion. Additionally, complexes I-III are air stable, insoluble in common organic solvents and can retain their crystalline integrity at ambient conditions for a considerable length of time.
In the IR spectra, a broad absorption centered at 3257 cm-1 for II is assigned to the stretch vibrations of v(O-H) and should be associated with the presence of water molecule. Weak absorptions appeared at 3062 (for I) and 3049 cm-1 (for both II and III) could be ascribed to the C-H stretching vibrations of aromatic
Table 1. Crystallographic data and structure refinement summary for I—III*
Parameter Value
I II I
Formula weight 634.94 1083.66 1676.56
Crystal size, mm 0.21 x 0.17 x 0.12 0.28 x 0.19 x 0.16 0.32 x 0.20 x 0.14
Crystal system Monoclinic Monoclinic Triclinic
Space group P2l/n P2 x/n P T
a, A 12.7557(9) 12.3986(6) 10.373(3)
b, A 14.0716(10) 16.0092(8) 12.222(3)
c, A 15.6135(11) 22.5151(12) 15.224(4)
a, deg 90.0 90.0 74.674(3)
P, deg 108.1690(10) 100.0420(10) 75.221(3)
Y, deg 90.0 90.0 71.348(3)
V, A3 2662.8(3) 4400.6(4) 1732.9(7)
Z 4 4 1
Pcalcd g/cm3 1.58
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